It is not "racist" to take into account skin colour when judging a situation.
For example, if you are on a dark street late at night, and at one end a group of three black youths are walking towards you, and at the other end three white youths are walking towards you, it is clearly sensible to walk towards the white youths since black youths carry out a disproportionally large amount of street crime.
Given that the percentage of young black females qualifying as doctors is considerably lower than the percentage of young white females or males qualifying as doctors, it would seem perfectly reasonable to be sceptical. If, however, the person produced evidence that they really were a doctor, but the airline refused to let them help, that would most certainly be racist.